Electromagnetic coils



Dec. 11, 1962 T. WROBLEWSKI ETAL ELECTROMAGNETIC COILS Original Filed April 15, 1954 2 Sheets-Sheet 1 INVENTORS THEODORE WROBLEWSK/ ALBERT ZACK ATTORN EY Dec. 11, 1962 T. WROBLEWSKI E'I'AL 3,068,433

ELECTROMAGNETIC coILs Original Filed April 15, 1954 2 Sheets-Sheet 2 T DORE WROBLEWSKI A B RT ZACK INVENTORS ATTORNEY States This, invention relates to electromagnetic coils, and particularly to spiral coils.

Anobject of the invention is to improve the permeabih ity and increase the inductance of such coils.

A further object is to insulate such coils, and yet another is to sealthe coils against moisture penetration.

These and other objects are accomplished by covering the coil with a mixture of ferromagnetic powders in av binder, such as a resin, lacquer, wax, glass or the like.

Other objects, features and advantages of the inven- 2 tion will-be apparent from the following specification, taken-in connection with the accompanying drawings, in which:

PEGURE lisaside view of a. coil according to the invention, but before the application. of the coating;

PlGURE 2 is a sectional View through the center, of a coated coil; and FIG. 3 is a side View of the coated coil.

FIGURE 4 is a view of oneembodiment of a transformer according to the invention.

FIGURE 5 is a cross-sectional view showing another embodiment of a transformer according to the invention.

FIGURE 6 shows a perspective view of one embodiment of a transformer according to the invention, partially cut away to show the various layers.

030 I CH n In FIG. 1, the strip 1 of a conducting material, for example copper, aluminum or the like, is wound into a spiral, with successive turns being spaced apart and insulated from each other by the concentric spiral strip 2 of insulating material, for example, insulating paper, resin or the like. The coil may be formed as in copending application Serial No. 401,333 filed December 30, 1953, by Albert Zack.

The coil can have a core-3-of ferromagnetic material, or it can-have an insulating core. The ferromagnetic aaterial is preferably aniron powder embedded in a resin such as epoxy, although other ferromagnetic cores can be used.

Around ,the coil, and preferably extending all around it to form a closed magnetic circuit, is a coating 4 of ferromagnetic powder, for example powdered iron, in a binder such as epoxy, resin, nylon, polystyrene, wax, shellac, varnish, polyethylene, laquer, glass ceramic or the like. The coating can be applied by dipping, spraying, painting or in any other convenient manner. The binder can then be dried, or set. If a material such as epoxy resin is used, the coil can be set in a form of the desired size and shape, and the epoxy resin cast about the coil.

The wafers are preferably supported by their leads '5, 6 and immersed in a dipping resin. After immersion, they are dried. The drying is done by pushing the leads into a piece of porous plastic, for example, Polarfoam, which can be mounted on a wooden piece fixed to a shaft which is rotated at a speed, for example, of three revolutions per minute. During the rotation, the wafers turn completely about their axis; this gives a uniform flow during drying. The rotation continues until the resin hardens, which generally takes from 4 to 12 hours.

3,068,433 Patented Dec. 11, 1962 ice The porous plastic can have a diameter or side of about 12 inches for convenience, and the coils can be set near the outer side of the material, the coils being supported about an inch or so from the porous plastic by their lead-in wires.

The dipping mixture in one example was the Minnesota Mining andManufacturing Companys Scotchcast Resin #2, a room temperature thermosetting epoxy resin, with a type Ccatalyst, various fillers being added to color the resin, to increase. its viscosity and to modify the electrical characteristics of thewafer. One such mixture is:

grams resin 30 grams powdered zinc oxide.

The zinc oxide serves to thicken the resin and to color it white. Other pigments can be used, especially where other colors are desired, for example, chromium oxide, cobalt oxide, carbon black, andiron oxide. Another mixture is:

grams resin. 20 grams of finely powdered iron. 20 grams of'finely powderedmica.

Theiron serves to increase the inductance of the wafer and to reduce the resonant frequency. The mica gives the resin the. necessary bulk.

The catalyst which can be ethylene diamine, or diethylene triamine, is preferably, about 10% by weight of the resin, tl e amount being preferably between 1 and 20%. The catalyst is added to the resin before the wafer coils are dipped into it.

The epoxy resin is a condensation polymer having the following typical structural formula:

The thickness of the coating 4' and the amount of ferromagnetic material in it can be varied to give the desired inductance or other results. The amount of ferromagnetic material can vary from a small amount, say a few percent by volume. of the coating, to nearly 100%.

it may be desirable in some cases, say for the reduction of leakage flux, to space the conductor at its sides from the magnetic coating. This can be done with an insulating washer or disk, or by first applying to the coil an insulating coating, of a. material such as those mentioned above forv use with the magnetic coating but without the magneticrnaterial. A coating of. insulating material con- .taining magnetic material can then be applied over the insulating coating;

Prior to the application of the coating, lead-in Wires 5 and 6 are attached to the ends of the spiralled conductor strip 1. This can be done in any convenient manner, for example by soldering. The soldering will be facilitated if, before winding the strip 2, one end is wrapped around a metal wire 11, parallel to the axis of the coil, and the other end of strip 2 is wrapped around a similar wire 12.

If a transformer is desired instead of an inductance coil, two of the coils can be placed side by side as shown in PEG. 4 preferably on a common core 10 of ferromagnetic powder, and the ferromagnetic coating 4 applied over the resultant double coil, 1-2, 78. Coating should not be applied between the coils unless a considerable amount of leakage reactance is desired. The coils can have different numbers of turns to give a different voltage ratio.

Instead of placing two coils side by side, one coil can be wound over another, with lead-in wires such as 5, 6

apes tee attached to the inner coil and lead-in wires 14, attached to the inner coil, as shown in FIG. 5. The outer diameter of the inner coil will be less than the inside diameter of the outer coil, the two being concentric.

Although the metal strip 2 is usually of aluminum, it can be of copper or other metal or conducting material. However, due to the space factor of the spiral coils of the invention, the use of aluminum will generally give as compact a coil as copper would, and often as low a resistance, together with a saving in weight. Similarly, although the insulating layer is usually of paper, it can be of other insulating material, and can even be a coating of insulating enamel, laquer, oxide, resin or the like on the metal conductor. If the conductor is aluminum, anodization of the aluminum can be provide the insulation, the anodization producing an oxide coating on the aluminum.

Two conducting strips separated by insulating strips can be wound in a bifilar manner, if desired, to form a transformer, as shown in FIG. 6. The metal strips 15, 16 and the insulating strips 17, 18 between them, are wound into concentric spirals and then covered with the coating 4. Lead-in wires 19, 20 are soldered to the strip 15, and lead-in wires 21, 22 to the strip 16, in the same manner that lead-in wires 5, 6, 14, 15 are in FIG. 5.

If desired, the core of the spiral may be left open, that is, so that the coil is annular in form, and if desired, a screw-threaded plug of ferromagnetic powder embedded in a binder can be screwed into said coii until the desired inductance or mutual inductance is attained.

In cases where it is desired merely to insulate the coils, a coating of insulating material alone, for example, of the insulating material specified above, may be applied to the coils. Whether or not a ferromagnetic powder is incorporated in the insulated material, a colored pigment may also be incorporated, to give the finished coil, a white, blue, red or other color. Diiferent colors can be used for dififerent types of coil, for example, a coil of one inductance could be white, of another inductance blue, and the like.

Zinc oxide or similar fillers in the coating will change the distributed capacity of the coil.

Where two coils are used, the capacity of the coil can be varied by changing the spacing between the coils or the dielectric constant of the spacing material 13. The inductance will also vary with the spacing.

This application is a division of applicants copending US. patent application, Serial No. 423,370, filed April 15, 1954, and issued on September 2, 1958 as US. Patent 2,850,707.

What we claim is:

1. An electromagnetic device comprising a substantially fiat, one-turn wide spiral of metal ribbon, at oneturn wide spiral of solid nonmagnetic insulating ribbon filling the space between the turns of said spiral, another one-turn wide-spiral or" metal ribbon, said other spiral be- 4 ing of larger diameter than said first spiral and concentric therewith and in the same plane therewith, a second oneturn spiral of solid nonmagnetic insulating ribbon filling the space between the turns of said second-mentioned spiral of metal ribbon, and a coating of ferromagnetic material over the outside surface of said combination of spirals.

2. The device of claim 1, in which the ferromagnetic material has an insulating binder and a coloring pigment mixed therewith.

3. An electromagnetic device comprising a substantially fiat, one-turn wide spiral of metal ribbon, a one-turn wide spiral of solid nonmagnetic insulating ribbon filling the space between the turns of said spiral, another one-turn wide-spiral of metal ribbon, said other spiral being of larger diameter than said first spiral and concentric therewith and in the same plane therewith, a second one-turn wide spiral of solid nonmagnetic insulating ribbon filling the space between the turns of said second-mentioned spiral of metal ribbon, and a coating of a coloring pigment in an insulating binder over the outside surface of said combination of spirals.

4. An electromagnetic device comprising two substantially fiat, one-turn wide spirals of metal ribbon concentric with each other and wound together in bifilar form, the ribbon of one spiral being separated from the ribbon of the other by having a one-turn wide spiral of solid nonmagnetic insulating ribbon on each side of the ribbon, and a coating of ferromagnetic material in an insulating binder over the outside surface of said combination of spirals.

5. The device of claim 4, in which the ferromagnetic material has an insulating binder and a coloring pigment mixed therewith.

6. An electromagnetic device comprising two substantially fiat, one-turn wide spirals of metal ribbon concentric with each other and wound together in bifilar form, the ribbon of one spiral being separated from the ribbon of the other by having a one-turn wide spiral of solid nonmagnetic insuiating ribbon on each side of the ribbon, and a coating of a coloring pigment in an insulating binder over the outside surface of said combination of spirals.

References Cited in the file of this patent UNITED STATES PATENTS 217,466 Le Conte July 15, 1879 2,457,806 Crippa Jan. 4, 1949 2,550,592 Pearce Apr. 24, 1951 2,604,519 Mackereth July 22, 1952 2,710,947 Gaston June 14, 1955 2,850,707 Wroblewski et a1. Sept. 2, 1958 2,856,577 Schmidt Oct. 14, 1958 FOREIGN PATENTS 550,963 Italy Nov. 14, 1956 

